Merge "Fix race condition in refreshing "join" task state"

mistral/engine/task_handler.py

@@ -409,6 +409,17 @@ def _refresh_task_state(task_ex_id):
 
         wf_ctrl = wf_base.get_controller(wf_ex, wf_spec)
 
+        with db_api.named_lock(task_ex.id):
+            # NOTE: we have to use this lock to prevent two (or more) such
+            # methods from changing task state and starting its action or
+            # workflow. Checking task state outside of this section is a
+            # performance optimization because locking is pretty expensive.
+            db_api.refresh(task_ex)
+
+            if (states.is_completed(task_ex.state)
+                    or task_ex.state == states.RUNNING):
+                return
+
             log_state = wf_ctrl.get_logical_task_state(task_ex)
 
             state = log_state.state